Is $299 on sale, has been slightly cheaper before but required eBay Plus or use of coupons.
Includes free shipping.
In before commenters do this for me, yes it's more expensive than other NVME SSDs but is currently the only way to play series X games using velocity architecture.
Any other SSD or normal HDD in an enclosure is only good enough for Xbox One and Xbox 360 games, however can act as storage of Series X/S games to save deleting re-downloading.
Given the E3 press conference this morning, I think it's a fair bet that a lot of Gamepass holders will be using the limit of their 1TB internal storage very shortly with upcoming releases coming to Gamepass on day 1.